From AHD
judder

SYLLABICATION: jud·der
PRONUNCIATION: jdr
INTRANSITIVE VERB: Inflected forms: jud·dered, jud·der·ing, jud·ders
To shake rapidly or spasmodically; vibrate conspicuously: “Edith would watch her wrestling with words, her thin little body juddering with the effort to unlock them” (Anita Brookner).
NOUN: A rapid or spasmodic shaking.
ETYMOLOGY: Perhaps j(erk)1 + (sh)udder.